- for this purpose, add new constructors and build_gradients method taking
a FieldMatrix and get "gradient" key from config as FieldMatrix

This reverts commit 23835015adb4ec41f3423a37e27f9ff43aebda38.

Conflicts:
	dune/stuff/test/grid_periodicview.cc
	resolved by using local version

- for this purpose, add new constructors and build_gradients method taking
a FieldMatrix and get "gradient" key from config as FieldMatrix

This reverts commit e52259a4b3c6f7b6ee6b3e97af9ffdc32eff20bb.

Conflicts (resolved to remote branch):
	dune/stuff/fem/customprojection.hh
	dune/stuff/fem/error.hh
	dune/stuff/fem/functionadapter.hh
	dune/stuff/fem/functions/checks.hh
	dune/stuff/fem/functions/integrals.hh
	dune/stuff/fem/functions/magnitude.hh
	dune/stuff/fem/functions/timefunction.hh
	dune/stuff/fem/localmatrix_proxy.hh
	dune/stuff/fem/restrict_prolong.hh

Conflicts:
	dune/stuff/discretefunction/projection/heterogenous.hh
	dune/stuff/grid/periodicview.hh